11498: fixed issues with Dockerfile-Dev (HabitRPG#11518)

Author: davis1410

.dockerignore

@@ -1,3 +1,2 @@
 node_modules
 .git
-website

Dockerfile-Dev

@@ -1,5 +1,11 @@
-FROM node:12
-WORKDIR /code
-COPY package*.json /code/
-RUN npm install
-RUN npm install -g gulp-cli mocha
+FROM node:12
+
+# Install global packages
+RUN npm install -g gulp-cli mocha
+
+# Copy Habitica code into container and install dependencies
+WORKDIR /usr/src/habitica
+COPY . /usr/src/habitica
+
+RUN npm install
+RUN npm run postinstall